1. Field of the Invention
The present invention relates to zoom lens systems, interchangeable lens apparatuses, and camera systems. In particular, the present invention relates to: compact and lightweight zoom lens systems having short overall length, and excellent optical performance with sufficiently compensated aberrations; and interchangeable lens apparatuses, and camera systems, each employing the zoom lens system.
2. Description of the Background Art
In recent years, interchangeable-lens type digital camera systems (also referred to simply as “camera systems”, hereinafter) have been spreading rapidly. Such interchangeable-lens type digital camera systems realize: taking of high-sensitive and high-quality images; high-speed focusing and high-speed image processing after image taking; and easy replacement of an interchangeable lens apparatus in accordance with a desired scene. Meanwhile, an interchangeable lens apparatus having a zoom lens system that forms an optical image with variable magnification is popular because it allows free change of focal length without the necessity of lens replacement.
Zoom lens systems having excellent optical performance from a wide-angle limit to a telephoto limit have been desired as zoom lens systems to be used in interchangeable lens apparatuses. Various kinds of zoom lens systems each having a negative lens unit located closest to an object side, and a multiple-unit construction have been proposed.
For example, Japanese Laid-Open Patent Publication No. 2008-040485 discloses a lens system having a two-or-more unit construction of negative and positive lens units. In the lens system, a diaphragm is located between a position on the image side of the first lens unit and an object side surface of a lens located closest to the image side in the second lens unit. The interval between the first lens unit and the second lens unit varies when the magnification varies. A shutter is located immediately on the image side of the second lens unit.
Japanese Laid-Open Patent Publication No. 2009-048012 discloses an optical system having a two-or-more unit construction of negative and positive lens units. In the optical system, at least one of a plurality of lens units includes a lens whose refractive index to the d-line and Abbe number to the d-line are set in specific ranges, respectively.
In each of the lens system and the optical system disclosed in the above-mentioned patent literatures, however, compensation of aberrations is insufficient. Therefore, none of these systems has excellent optical performance. Furthermore, the construction of the lens unit having negative optical power and located closest to the object side makes it difficult to reduce the overall length of lens system. Thus, size reduction which is recently demanded is not achieved.